// 基于下面提供的代码，完成后续的四个练习
class Container {
    static of (value) {
        return new Container(value)
    }

    constructor (value) {
        this._value = value
    }

    map (fn) {
        return Container.of(fn(this._value))
    }
}

class MayBe {
    static of (x) {
        return new MayBe(x)
    }

    isNothing () {
        return this._value === null || this._value === undefined
    }

    constructor (x) {
        this._value = x
    }

    map (fn) {
        return this.isNothing() ?this : MayBe.of(fn(this._value))
    } 
}
module.exports = { MayBe, Container }